The Parish of St Andrew, Avonmouth

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In praise of engineering

Originally built in 1893, then bombed and burnt out in 1941, the Parish Church of St Andrew was re-built in 1957, and will now be undergoing a major facelift.

Part one of the facelift will be a 6m high galvanised steel cross, to be installed on the roof of the 12m high church tower, lit with floodlights.

RISE came up with two solutions which avoided noisy resonance and reverberation caused by the frequency of the wind on this site, very close to the coast. The chosen design will use 15 thick 100 wide angles and 10 thick plate steel which will be welded together, allowing the cross to have resistance to the wind and achieving 3% thickness to height ratio.

The tower roof happens to be constructed of a reinforced concrete slab, with a flagpole aperture already in place, and steel beams supporting it. RISE managed to confirm that the existing structure can take the weight and wind load of the new cross without strengthening up, saving money and time for the client. RISE surveyed the steel beams on site, and designed a new shoe to fix the base of the cross into, supported by the steel beams within the tower.

The whole cross will need to be constructed in one piece and double dip galvanised. Talking to a local steelwork contractor, the cross will be installed by crane onto the tower rooftop, lowered directly into the pre-existing flagpole aperture, and will be fitted and fixed into the newly designed shoe, at the point where the beams cross.

RISE designed new tie fixings with high tensile steel cable, to be fixed into the reinforced concrete slab at roof level, as well as into the existing steel beams below the tower roof.

It will be very exciting to see this on site, and to continue assessing its vibration once installed. Structure doesn’t have to be all about building, and it will be great to see our ingenuity put to the test.